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Is the periodic table WRONG? Elements may need to be reordered after scientists find lawrencium looks out of place

Press/Media: ResearchPopular

10/04/2015

Publication in the Daily mail concerning our article in Nature on the measurement of the first ionization potential of lawrencium (Nature 520, 209 (2015), cover page feature).

 

 

  • The Japan Atomic Energy Agency has studied lawrencium for the first time
  • The element is extremely difficult to make and has a half life of 27 seconds
  • They found it is different from other rare radioactive elements in the f-block
  • It is likely to fuel the debate for lawrencium to be in the main body of table

 

      

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It has been a key part school chemistry lessons for more than a century, but now the periodic table may need to be redrawn after scientists found a rare element may be very different from originally thought.

Researchers have for the first time been able to test how much energy is required to strip an electron from an atom of the radioactive element lawrencium.

The rare metal currently sits at the very bottom of the periodic table at the end of a group of elements known as the actinides, which sit in a separate block from the main table.

But the results of new research suggest the element may have properties similar to sodium and potassium, which may fuel arguments that it would be better placed in the main body the periodic table.

Lawrencium, marked as Lr on the periodic table above, currently sits in a separate block from the main table

Lawrencium, marked as Lr on the periodic table above, currently sits in a separate block from the main table

If it is redraw, it means that chemistry students could have to relearn the order of how the elements appear. 

Lawrencium, which was first discovered in 1961 by the nuclear scientist Ernest Lawrence, is notoriously difficult to make and only exists for a few seconds at a time.

This has made the element, which can only be generated in particle accelerators, extremely difficult to study.

THE SWELLING PERIODIC TABLE 

There are several newly discovered atoms that currently do not appear on the periodic table.

Two years ago scientists claimed to have discovered the existence of a new atom with an atomic number of 115.

This makes it one of the heaviest chemical elements detected to date and does not occur naturally.

Instead scientists had to synthesis it in the laboratory by bombarding a film of another heavy element known as americium with calcium ions.

The resulting element lasted for just a fraction of a second before it decaying into more commonly found elements.

Although still to be officially named, it has been given the temporary name of ununpentium.

The International Union of Pure and Applied Chemistry has also recently announced that nineteen elements have had their atomic weights reassessed.

 

Among those to have had their standard atomic weights adjusted are elements like aluminium, fluorine, arsenic, caesium, cadmium and selenium.

While some of the atoms were found to have an average weight that was a tiny fraction greater than previously calculated, others decreased.

Overall the total atomic weight displayed on the periodic table increased by 0.003640021 as a result of the changes.

But now researchers at the Japan Atomic Energy Agency have been able to create enough to measured the ionisation potential of lawrencium for the first time.

Speaking to Chemistry world, Yuichiro Nagame, a researcher at the Japan Atomic Engery Agency who took part in the study, said: ‘[Lutetium and lawrencium] – the last column of lanthanides and actinides – could be put into the group III column of the periodic table, under scandium and yttrium.’

The current structure of the periodic table was drawn up in 1945 after the Nobel-prize winning chemist Glenn Seaborg suggested the actinides - rare radioactive elements - belonged in a separate part of the table which is known as 'f-block'.

However, some chemists have argued that placing lawrencium at the end of this block was incorrect and they should be put in the 'd-block' of the main table.

Dr William Jensen, a chemist at the University of Cincinnati, argues that along with lutetium, lawrencium is misplaced in the f-block.

In a paper published in the journal Foundations of Chemistry last month, he said: 'Though there are many misconceptions concerning the nature and function of the periodic law and table, perhaps the most prevalent among modern chemists is the belief that the periodic table is nothing more than an electron configuration table.

'While there is certainly a significant correlation between electron configurations and chemical periodicity, the correlation is far from perfect.

'Lutetium and lawrencium, rather than Lanthanum and Actinium, should be assigned to the d-block as the heavier analogs of Scandium and Yttrium, whereas Lanthanum and Actinium should be considered as the first members of the f-block with irregular configurations.'

Lawrencium is represented by the diagram above which shows the electron shells of the atom
Ernest Lawrence, a nuclear physicist, discovered lawrencium after creating it in the laboratory in 1961
 

Lawrencium, represented by the diagram left, was discovered by nuclear scientist Ernest Lawrence (right)

Lawrencium was first generated by Ernest Lawrence by bombarding californium atoms with boron atoms to create the new superheavy element.

However, scientists have only ever been able to produce minuscule amounts of the substance and it has a half life of 27 seconds.

The new study, which is published in the journal Nature, used the same approach as Lawrence to create the element that bears his name but captured it in a helium and cadmium iodide gas.

This was passed through a heated tantalum surface giving the short-lived lawrencium enough energy to shed its outer electron - the ionisation potential.

The researchers found this matched a recent prediction of 4.96eV - giving it the lowest ionisation potential of all elements in the f-block.

This representation of the periodic table shows the ionisation potential of elements following the new results

This representation of the periodic table shows the ionisation potential of elements following the new results

However, in a statement, the Japan Atomic Energy Agency said it did not feel it affected the structure of the periodic table.

They said: 'Since the introduction of the 'actinide concept' as the most dramatic modern revision of the Periodic Table of the Elements by Glenn Seaborg in the 1940s, the element with atomic number 103, lawrencium (Lr), played a crucial role as the last element in the actinide series.

'We show that removing the outermost electron requires least energy in Lr among all actinides, as was expected. T

'This validates the position of Lr as the last actinide element and confirms the architecture of the Periodic Table.'

However, Dr Eric Scerri, a chemist and historian at the University of California Los Angeles, said the results supported the push to move lawrencium into the min part of the table.

He said: 'If the periodic table is presented in the more correct 32-column or long-format, and if one maintains the order of increasing atomic numbers throughout the table, one is inevitably led to the conclusion that Lu and Lr belong to group 3 and that La and Ac should be placed at the start of the f-block elements.' 

Despite the debate the result is likely to now generate, Professor Andreas Türler, a chemist at the Albert Einstein Centre for Fundamental Physics at the University of Bern, Switzerland, described the experiment as 'spectacular'.

The researchers were able to study lawrencium for the first time using an ionizer cavity
The study revealed that the element has one of the lowest ionisation potentials of any of the atoms in the f-block
 

The researchers were able to study lawrencium for the first time using an ionizer cavity (left) which revealed that the element has one of the lowest ionisation potentials of any of the atoms in the f-block (righ



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References

Related Publications
  1. Measurement of the first ionization potential of lawrencium, element 103

    Sato, T. K., Asai, M., Borschevsky, A., Stora, T., Sato, N., Kaneya, Y., Tsukada, K., Duellmann, C. E., Eberhardt, K., Eliav, E., Ichikawa, S., Kaldor, U., Kratz, J. V., Miyashita, S., Nagame, Y., Ooe, K., Osa, A., Renisch, D., Runke, J., Schaedel, M., Thoerle-Pospiech, P., Toyoshima, A. & Trautmann, N., 9-Apr-2015, In : Nature. 520, 7546, p. 209-U153 4 p.

    Research output: Contribution to journalArticleAcademicpeer-review

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